Updated: 5:05 p.m. | A bipartisan group of 50 senators urged appropriators Thursday to include a provision in year-end, catchall spending legislation that would prevent the U.S. Post Office from closing more mail-processing facilities in the next fiscal year.

“This one-year moratorium will give Congress the time it needs to enact the comprehensive postal reforms that are necessary for the Postal Service to function effectively into the future,” the group said in a letter to Appropriations Committee Chairman Barbara A. Mikulski, D-Md., and ranking member Sen. Richard C. Shelby, R-Ala.

The letter — circulated by Sen. Bernard Sanders, I-Vt., Sen. Tammy Baldwin, D-Wis., and Sen. Jon Tester, D-Mont. — was also sent to Sen. Tom Udall, D-N.M., chairman of the Financial Services Appropriations Subcommittee, which has jurisdiction over the post office, and the panel’s ranking member Sen. Mike Johanns, R-Neb.

While Congress doesn’t provide funding for the post service, it does oversee the agency. The letter comes as the post office has been hemorrhaging money in recent years. The agency reported Monday that it lost $2 billion in the second quarter, and $740 million compared to the same time last year. The post office has recorded a loss in 21 of the last 23 quarters. However, the USPS did report a $327 million, or 2 percent, increase in operating revenue due, in part, to continued growth in package delivery.

Congress has sought to reform the post office, but has failed to enact any legislation — including a controversial request from the agency to cut Saturday mail delivery as a cost-saving measure.

So without congressional reform, the post office has already consolidated 141 mail-processing facilities since 2012 and more closures are expected, which the bipartisan group wants to halt by including a provision on the omnibus or continuing resolution Congress is likely to pass before the Sept. 30 end of the fiscal year.

“In the absence of Congressional compromise, the Postal Service will propose more sweeping changes to its operations,” the letter warned.

“The Postmaster General has announced that the postal service will consolidate up to 82 more mail processing facilities and eliminate up to 15,000 more jobs in 2015,” the letter said. “This wave of closures will directly impact 37 states across our nation, and more importantly, the citizens who on the postal service to be reliable.”

The senators also called for additional language that would continue service standards for first-class mail and periodicals as of July 1, 2012, which they contend are at risk of being weakened to reduce costs.

A USPS spokesman said that congressional reform would be the best course of action, and stressed that failing that, the Postal Service should be allowed to continue to make its operations more efficient.

"We are disappointed by the recent effort to block our ongoing initiative to remove excess capacity from our mail processing network," said Dave Partenheimer a USPS spokesman. "It would be unfortunate if this action were to impede our current progress. A comprehensive legislative package is the most appropriate way to address our systemic business model and financial issues."

Most of the 50 signatories to the letter were Democrats, but six were Republicans: Sens. Roy Blunt of Missouri, John Hoeven of North Dakota, John Thune of South Dakota, Susan Collins of Maine, James M. Inhofe of Oklahoma, and Orrin Hatch of Utah.